The present invention relates to an optical information processor capable of processing signals at high speed and at high recording density.
Hitherto, in applications of an optical information processor, in order to read/record high-density information (optical memory) from/to a recording medium such as an optical disk, it is indispensable to shorten the wavelength of a semiconductor laser as a light source. As an example of conventional techniques, a blue-violet laser having the shortest wavelength out of semiconductor laser devices is described in Japanese Journal Applied Physics Letters, Vol. 35, 1996, pp. L74 to L76.
The conventional technique, however, can utilize the features of only the light source and does not contribute to reduction in size and weight of an optical head including optical devices such as a light-emitting device and a light-receiving device and an optical system in an optical pickup mechanism. The conventional technique does not have a system configuration for processing an optical signal by near-field recording which converges a laser beam emitted from a light-emitting device to a near field pattern by an integrated focusing lens and forms a very small spot on a recording medium (optical recording medium). In the near-field recording, information can be recorded/read to/from a memory smaller than that determined by the wavelength of a laser beam and the numerical aperture of an optical system lens, so that recording of higher density can be achieved.
The conventional technique uses the configuration of an existing optical head and cannot achieve reduction in size and weight of an optical head and address to a demand of higher processing speed. Consequently, the features of only the light source do not contribute to a higher-speed access of an optical information processor.
FIG. 26 is a schematic diagram showing a conventional optical pickup mechanism. A transmission beam (laser beam) 13 emitted from a light-emitting device (semiconductor laser device) 7 sequentially passes through a polarized light separating diffraction grating 6 and a xcex/4 wave plate 5. An optical path 10 is changed by a beam splitter 4 and also by a reflecting mirror 3. The beam passes through an objective lens 2 and is focused on a recording surface of a recording medium (optical recording medium, disk) 1 to form an image. A reflected beam 24 reflected by the recording medium 1 passes through the objective lens 2 and is reflected by the reflecting mirror 3 and passes through the beam splitter 4. After that, the beam is condensed by a condenser lens 8 onto a light-receiving face of a light-receiving device 9.
As described above, the conventional optical pickup mechanism is constructed by discrete optical devices and the optical devices are optically connected via a space, so that the volume is large and weight is heavy. The dimensions of the mechanism are, for example, about 60xc3x9740xc3x9710 mm.
The inventor herein has found that a small, light optical head can be formed by integrating a light-emitting device (semiconductor laser) and a light-receiving device on the same substrate in a flat shape, allowing a laser beam (transmission beam) emitted from the light-emitting device to travel perpendicular to a substrate face, and integrating a diffraction light separating device and a condensing device (lens) hierarchically in the direction perpendicular to the substrate.
It was also confirmed that, with the configuration, by designing each of the devices in consideration of the outgoing direction of the transmission beam and reception of a condensed beam and a diffracted beam, an optical information processor capable of recording/reproducing information to/from a recording mark in a recording medium by near-field recording which converges a beam to a near-field pattern and diffraction beam splitting control, and performing high-density recording and reproduction at high speed which cannot be achieved by the conventional techniques can be achieved.
An object of the invention is to provide an optical information processor capable of recording information at high recording density and reproducing the information at high speed.
The above and other objects and novel features of the invention will become apparent from the description of the specification and the appended drawings.
The outline of representative ones of inventions disclosed in the application will be briefly described as follows.
(1) An optical information processor having a light-emitting device, a light-receiving device, and a plurality of optical devices positioned in an optical path and for controlling light, constructing an optical system for forming an image on a recording face of a recording medium by a transmission beam emitted from a front light-outgoing end of the light-emitting device and for forming an image on a light-receiving face of the light-receiving device by a reflected beam reflected by the recording face, and reproducing information recorded on the recording medium and/or recording information to the recording medium, including: a substrate having, on one face thereof, a light-emitting device (semiconductor laser device) for emitting a transmission beam in an in-plane direction and a plurality of light-receiving devices for receiving reflected beams of the transmission beam from the inside of the plane, which is made of a base material capable of forming the light-emitting device and the light-receiving devices by crystal growth and an insulating material through which the transmission beam and the reflected beam pass; a diffraction light separating device stacked on the other face of the substrate, for correcting and changing an optical path so that the reflected beams from the recording medium are received by the light-receiving device; a xcex/4 wave plate stacked on the diffraction light separating device; and a dielectric plate stacked on the xcex/4 wave plate, constructing a lens for converging the transmission beam onto a recording face of the recording medium and converging the reflected beam from the recording medium onto the substrate side.
The substrate, the diffraction light separating device, the xcex/4 wave plate, and the dielectric plate are integrated mechanically and physically, and construct an optical head attached to a suspension arm of an optical pickup mechanism of an optical information processor. The optical head is light to an extent that it can bear a high-speed swing. The substrate, the diffraction light separating device, the xcex/4 wave plate, and the dielectric plate are bonded by an intermolecular force of thermo compression bonding under high vacuum of about 10xe2x88x929 to 10xe2x88x9210 Torr.
The lens is constructed so as to form an image as a near field image on a recording face of a recording medium by the transmission beam and to reproduce/record information of near-field recording from/to the recording medium. The near field image is formed in a range from a few nm to a few hundreds nm from the surface of the dielectric plate.
Each of the lens and the diffraction light separating device is formed by a diffraction grating, when a diffraction grating lens is used as the lens, the reflected beam is diffracted to generate a primary diffracted beam, the diffracted primary beam is separated via the diffraction light separating device, and separated beams are received by the light-receiving devices. The diffraction grating is constructed by at least two kinds of areas having different refractive indices and is, desirably formed in a crystal having high anisotropy. At least two kinds of areas having different refractive indices in the diffraction grating are formed by diffusion of an impurity or ion implantation.
The light-emitting device is a semiconductor laser formed from a semiconductor crystal as a base formed by selective growth using an insulating mask on one face of the substrate, an active layer for emitting a laser beam from its end face is disposed along a direction perpendicular to one face of the substrate on which the light-emitting device is provided, and induced-emission light is resonated and amplified in a direction perpendicular to the substrate face. A reflection film is provided at both ends of the active layer of the light-emitting device, the reflection film of the front light-outgoing end of the active layer is constructed by the insulating mask used for selectively growing a semiconductor crystal on one face of the substrate, and reflectance of the reflection film at the front outgoing end is lower than that of the reflection film of the other end. The active layer of the light-emitting device has a multi-quantum-well structure or a strained multi-quantum-well structure obtained by introducing a lattice distortion into a quantum well layer.
A light-receiving area of the light-emitting device is a face-type light-receiving area or a waveguide type light-receiving area. The light-receiving device is formed by using a semiconductor crystal as a base formed by selective growth using an insulating mask on one face of the substrate. The light-emitting device and the light-receiving device are formed monolithically on the substrate.
(2) In the configuration of (1), the substrate, the diffraction light separating device, the xcex/4 plate, and the dielectric plate are bonded by a transparent bonding material.
(3) In the configuration of (1) or (2), a reflector for reflecting a peripheral portion of the transmission beam emitted from the light-emitting device is provided between the diffraction light separating device and the xcex/4 wave plate, a light-receiving device for detecting an optical output of the transmission beam is provided on one face of the substrate, and the reflected beam of the transmission beam reflected by the reflector falls on a light-receiving face of the light-receiving device for detecting the optical output of the transmission beam.
(4) In the configurations of (1) to (3), a modulator for controlling the transmission beam emitted from the light-emitting device is provided on the substrate portion at the front light-outgoing end side of the light-emitting device.
(5) In the configurations of (1) to (4), the substrate, the diffraction light separating device, the xcex/4 plate, and the dielectric plate are formed monolithically.
According to the means (1), the following effects are produced.
(a) In the optical head of the optical information processor, the transmission beam emitted from the front light-outgoing end of the light-emitting device (semiconductor laser device) sequentially passes through the substrate, diffraction light separating device, xcex/4 wave plate, and dielectric plate having the lens to form an image on the recording face of the recording medium (optical recording medium). The reflected beam reflected by the recording face goes back through the optical path through which the transmission beam has passed. The phase of the reflected beam is changed by the xcex/4 wave plate, and the phase-changed reflected beam is separated into two primary diffracted beams in two directions. The primary diffracted beams fall on the light-receiving faces of the respective light-receiving devices. Thus, information can be reproduced and/or recorded by near-field recording.
(b) The substrate having the light-emitting device and the light-receiving device, diffraction light separating device, xcex/4 wave plate, and dielectric plate having the lens are sequentially hierarchically integrated, and mechanically, physically integrated. Thus, the optical head having the functionality which cannot be realized by the conventional techniques and realizing small size and light weight can be provided. For example, the dimensions of the optical head can be set to 5 mm, 5 mm, and 9 mm. In the structure where the optical head is attached to the suspension arm of the optical pickup mechanism, therefore, the suspension arm can be swung at high speed like the head of a hard disk, and recording and reproduction can be performed at high speed also in the optical information processor (DVD drive).
(c) Since the substrate having the light-emitting device and the light-receiving device, diffraction light separating device, xcex/4 wave plate, and dielectric plate having the lens are integrated mechanically and physically, the optical path can be made extremely short, so that efficiency for utilization of the laser beam can be improved remarkably. By the reduction in the optical path, an access time of focus/tracking correction and reading (reproduction) with respect to the recording mark in the optical recording medium can be shortened, so that the higher-speed optical information process can be achieved.
(d) Since the substrate having the light-emitting device and the light-receiving device, diffraction light separating device, xcex/4 wave plate, and dielectric plate having the lens are integrated mechanically and physically, no air exists in the optical paths of the transmission beam and the reflected beam, so that the optical loss can be suppressed very much. Thus, improved transmission beam output of the semiconductor laser device and increased light-receiving sensitivity of the light-receiving device can be achieved. Particularly, in the structure that the substrate, diffraction light separating device, xcex/4 wave plate, and dielectric plate are bonded by an intermolecular force, an optical loss is smaller, and improved transmission beam output and increased light-receiving sensitivity of the light-receiving device are achieved, thereby increasing the performance of the optical information processor.
(e) By the above-described (c) and (d), in the optical pickup mechanism in the optical information processor, by the shortened optical path and reduced optical loss, the laser beam output can be lowered. Thus, power consumption for laser oscillation can be lowered.
(f) Since the near field recording can be performed, higher-density recording of the optical information processor can be achieved.
(g) As each of lens and the diffraction light separating device is formed by the diffraction grating having two kinds of areas formed by impurity diffusion or ion implantation, the devices can be easily fabricated with high precision, and lower cost of the optical head can be achieved.
(h) The light-emitting device (semiconductor laser device) and the light-receiving device can be formed monolithically on the substrate by the semiconductor manufacturing technique. Consequently, they can be fabricated with high precision at low cost and lower cost of the optical head can be achieved.
(i) Since the reflectance of the reflection film of the front light-outgoing end of the semiconductor laser device (light-emitting device) is lower than that of the reflection film at the other end, improved optical output of the transmission beam can be achieved. The reflection film at the front light-outgoing end is formed by an insulating mask used at the time of forming the semiconductor crystal by selective growth to form the semiconductor laser device, reduction in the manufacturing cost can be achieved.
(j) The semiconductor laser device has a multi-quantum-well structure or a strained multi-quantum-well structure obtained by introducing grating distortion into a quantum-well layer, a higher output of the laser beam can be achieved.
(k) The light-receiving area of the light-receiving device has a face-type light-receiving area or the waveguide type light-receiving area. Consequently, a reflected beam can be efficiently detected as a reception signal. Thus, on the basis of detection signals of the light-receiving devices, focus correction, tracking correction and, further, optical output control of the transmission beam can be carried out, and the optical information processor having high controllability can be provided.
According to the means of (2), effects similar to those of the configuration of (1) can be produced.
According to the means of (3), in addition to the effects of the configurations (1) and (2), since the laser beam portion emitted from the semiconductor laser device and is not converged on the recording face of the recording medium is reflected by the reflector provided between the diffraction light separating device and the xcex/4 wave plate and the reflected beam is detected by the light-receiving device for detecting an optical output, the optical output control (APC control) of the laser beam can be effectively performed.
According to the means of (4), in addition to the effects by the configurations (1) to (3), the transmission beam emitted from the semiconductor laser device can be controlled by the modulator.
According to the means of (5), in addition to the effects by the configurations (1) to (4), since the substrate, diffraction light separating device, and xcex/4 wave plate are monolithically formed, the optical loss in the interfaces of the substrate, diffraction light separating device, and xcex/4 wave plate becomes extremely small. Thus, improved efficiency for laser beam utilization is achieved.